1. Field of the Invention
The present invention relates to providing fault tolerant power to a computer system, and more particularly, to a control system for controlling the distribution of power to central processing units of the computer system.
2. Description of the Related Art
With the ever increasing amount of data being processed by today's computer systems, it is often desirable to have a mass storage subsystem to transfer large amounts of data to and from the computer system. Such a mass storage subsystem is commonly found in a local area network (LAN), wherein information and files stored on one computer, called a server, are distributed to local work stations having limited or no mass storage capabilities.
Because the work stations depend on the server for furnishing their mass storage needs, it is crucial the server remains on-line. A circuit of the server typically having a relatively low reliability and short lifetime is a AC-DC converter or adaptor which is used to regulate and furnish power to components of the server.
To compensate for its relatively short lifetime, redundant AC-DC converters are used, so that if one converter fails, uninterrupted power is still furnished to the server. More particularly, each central processing unit (CPU) of the server might have more than one AC-DC converter furnishing its power in order to ensure reliability for the LAN.
Because of the high operating frequencies and performance required of modern CPUs, minor variations in the fabrication of the CPU affect the performance of the CPU. It has been discovered that optimal performance of the CPU often occurs at a specific supply voltage level. In those cases, each CPU is tested by the manufacturer and assigned a required supply voltage level.
One such CPU is the Pentium Pro microprocessor manufactured by Intel. Each Pentium Pro microprocessor is tested by the manufacturer to find its optimal supply voltage level. Computer systems or servers incorporating the CPU must furnish this supply voltage level to the CPU. Thus, if the server has several CPUs, several different CPU supply voltage levels may be required.
If more than one CPU is located in the server, a problem arises in providing fault tolerant power to the multiple CPUs because each CPU might require a different supply voltage level. Thus, redundant power for all of the CPUs cannot be provided by paralleling all of the DC-DC converters which provide the variable supply voltage to the CPUs as they furnish different output voltage levels for different CPUs.
Furthermore, the fault tolerant power system furnished by parallel DC-DC converters cannot be extended to the situation in which only one DC-DC converter is operational and more than one CPU requires power from the single converter. Typically, each DC-DC converter is sized to power only one CPU in its normal mode of operation. Thus, attempting to preserve the functionality of more than one CPU from a single DC-DC converter results in the shutdown of the converter and the server.